This invention relates to high speed CMOS integrated circuits, and specifically to the incorporation of an irradiated relaxed SiGe layer in such an IC.
In enhanced mobility MOSFET device applications, thick, relaxed Si1-xGex buffer layers have been used as virtual substrates for thin, strained silicon layers to increase carrier mobility for both NMOS, K. Rim et al., Strained Si NMOSFETs for High Performance CMOS Technology, 2001 Symposium on VLSI Technology Digest of Technical Papers, p. 59, (IEEE 2001), and PMOS, Deepak K. Nayak et al., High-Mobility Strained-Si PMOSFETs, IEEE Transactions on Electron Devices, Vol. 43, 1709 (1996), devices. Compared with bulk silicon devices, enhancement in electron mobility of 70% for devices with Leff less than 70 nm have been reported, Rim et al., supra. Enhancements of up to 40% in high-field hole mobility for long-channel devices have also been reported. Nayak et al., supra. The predominant technique currently in use to produce a high quality relaxed Si1-xGex buffer layer is the growth of a several xcexcm thick, compositionally graded, layer, Rim et al. and Nayak et al., supra. However, the density of threading dislocations using this technique is still high, e.g.,  greater than 106 cmxe2x88x922. In addition, the integration of a several xcexcm thick Si1-xGex layer into MOS device fabrication is not very practical because of high fabrication costs.
Alternative methods to efficiently relax strained SiGe layers on silicon have been attempted, based on the SmartCut(trademark) process, employing atomic hydrogen implantation, M. K. Weldon et al., On the Mechanism of the Hydrogen-Induced Exfoliation of Silicon, J. Vac. Sci. Technol. B. 15, 1065, (1997), for the fabrication of high-quality silicon-on-insulator (SOI) wafers, atomic hydrogen (H+) implantation, followed by an appropriate anneal, has been used to increase the degree of SiGe relaxation and to reduce the density of threading dislocations, S. Mantl et al., Strain Relaxation of Epitaxial SiGe Layers on Si(100) Improved by Hydrogen Implantation, Nuclear Instruments and Methods in Physics Research B 147, 29, (1999), and U.S. Pat. No. 6,464,780 B1, granted Oct. 15, 2002, to Mantl et al., for Method for the Production of a Monocrystalline Layer on a Substrate with a Non-Adapted Lattice and Component Containing One or Several such Layers, H. Trinkaus et al., Strain Relaxation Mechanism for Hydrogen-Implanted Si1-xGex/Si(100) Heterostructures, Appl. Phys. Lett., 76, 3552, (2000), and the above-identified related U.S. patent application. Helium implantation, followed by an anneal step, has also been explored to promote relaxation in SiGe films, M. Luysberg et al., Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1-xGex Buffer Layers on Si(100) substrates, Journal of Applied Physics, Vol. 92, No. 8 (2002).
In addition to the SmartCut(trademark) process, another method for splitting wafers for SOI fabrication is the co-implantation of boron and H2+ ions, U.S. Pat. No. 5,877,070, granted Mar. 2, 1999, to Goesele et al., for Method for the Transfer of Thin Layers of Monocrystalline Material to a Desirable Substrate. Based on this, some of us have proposed the use of boron and H+ to relax SiGe films. Additionally, H+ has also been co-implanted with He for the purpose of SOI fabrication, Aditya Agarwal et al., Efficient Production of Silicon-on-Insulator Films by Co-implantation of He+ with H+, Proceedings of the 1997 IEEE International SOI Conference, p. 44, (1997).
All known methods which use the implantation of hydrogen to promote relaxation of strained SiGe layers have utilized ionized atomic hydrogen, H+. However, this implantation process is very expensive because of the long time required for the implantation process. The use of singly ionized molecular hydrogen, H2+, has been suggested to reduce the time and cost because the implantation would be done at twice the energy and half the current required for H+ implantation, Huang et al., and G. F. Cerofolini et al., Hydrogen-related Complexes as the Stressing Species in High-fluence, Hydrogen-implanted, Single-crystal Silicon, Physical Review B, vol. 46, p. 2061 (1992). Moreover, co-implantation of boron and singly ionized molecular hydrogen, H2+, has been shown to be effective for SOI fabrication, U.S. Pat. No. 5,877,070, and Huang et al. It follows, therefore, that the implantation of H2+ alone, U.S. Pat. No. 6,562,703 B1, to Maa et al., granted May 13, 2003, for Molecular hydrogen implantation method for forming a relaxed silicon germanium layer with high germanium content, or with boron, helium, silicon, or other species, for the purpose of relaxing strained SiGe films deposited epitaxially on silicon substrates should achieve desirable results.
Nova Cut(trademark) is a technique for film splitting after hydrogen implantation in the fabrication of SOI materials, Jason T. S. Lin et al., Nova Cut(trademark) Process: Fabrication of Silicon-on Insulator Materials, 2002 IEEE International SOI Conference, Williamsburg, Va., (2002), U.S. Pat. No. 6,486,008 B1, granted Nov. 26, 2002, to Lee, for Manufacturing Method of a Thin Film on a Substrate. This process is very similar to the SmartCut(trademark) process, however, the splitting is facilitated by microwave energy instead of heating. The Nova Cut(trademark) technique, however, is only usable for SOI wafer fabrication. SiGe relaxation through application of microwave energy is not known to have been proposed.
A method of forming a SiGe layer having a relatively high Ge content includes preparing a silicon substrate; depositing a layer of strained SiGe to a thickness of between about 100 nm to 500 nm, wherein the Ge content of the SiGe layer is equal to or greater than 20%, by molecular weight; implanting H2+ ions into the SiGe layer; irradiating the substrate and SiGe layer, to relax the SiGe layer; and depositing a layer of tensile-strained silicon on the relaxed SiGe layer to a thickness of between 5 nm to 30 nm.
It is an object of the invention to provide a thick, relaxed, smooth SiGe film with high Ge content as a buffer layer for a tensile strained silicon film to be used for high speed MOSFET applications.
Another object of the invention is to provide high quality, low defect density relaxed SiGe film.
Another object of the invention is to produce a relaxed SiGe layer from a strained SiGe layer by hydrogen implantation plus microwave irradiation.
A further object of the invention is to provide better control of total irradiation time without temperature ramping-up and ramping-down.
Yet another object of the invention is to perform SiGe relaxation at low temperature.
Another object of the invention is to control the size and distribution of micro-H2 bubbles, or cavities, to initiate the formation of dislocations.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.